Recipe Instructions With an electric mixer beat together butter, sugar and salt until very light, about 5 minutes on medium speed. Beat in egg until smooth. Mix baking soda with milk and add to batter. Remove from mixer, sift in flour and cocoa and stir to blend. Divide dough in half and shape into two 8-inch long cylinders, forming them in sheets of parchment paper. Chill until firm. Preheat oven to 325 degrees. Slice cylinders into 1/4-inch thick slices and arrange on parchment-paper lined baking sheets. Bake 15 to 20 minutes. This recipe yields 64 cookies.